The treatment of abnormal tissue masses (e.g., fibroids and tumors) which grow in proximity to healthy tissue often involves the destruction of tissue. For example, local ablation of a tissue mass may be carried out by inserting a therapeutic device thereinto to destroy the targeted cells. For example, electrical energy may be applied to the tissue mass by placing one or more electrodes into the tissue mass and discharging electric current therefrom to ablate the tissue. Alternatively, fluids with appropriate properties may be injected into the vicinity of the tissue mass to chemically necrose selected portions of tissue.
When electric energy is used to ablate tissue, the size and shape of the region of tissue ablated depends, in part, on the configuration of the electrodes used for the procedure and, in part, on the strength of the charge applied. The energy received by the tissue dissipates rapidly as the distance from the electrode increases making it difficult to maintain a high level of energy density within a large volume of tissue. Therefore, the ablation of large tissue masses often requires a multi-step process with electrodes placed in an initial location for a first ablation and then re-inserted to a second location for further ablation with additional repetition of these steps as required. This increases the complexity and duration of the procedure with corresponding increases in patient discomfort and cost.
Another drawback of electrical ablation procedures is that the coupling between the tissue and the electrodes degrades as the procedure is carried out because, during the procedure, tissue in direct contact with the electrodes becomes desiccated and loses its conductivity. The electrodes thus become surrounded by high impedance tissue, preventing energy from reaching more distant tissue.